Add advice about the recommended nodejs version of the project and a short explanation about nvm on main readme, chapter 4 and exercises readme

Author: Ferran Llop

README.md

@@ -53,9 +53,39 @@ Find pre-generated **PDF** and **EPUB** as [build artifacts of the latest releas
 
 > ⚠️ This project setup is now a bit old and thus, you may run into various issues when building this locally. We recommend to use node v10.22.1 and the latest version of Calibre if possible. 
 
+### About the nodejs version
+
+As the recommended node version (v10.22.1) is a bit old now, is more than likely that you do not have it installed on your system. You can have multiple versions of nodejs installed on your system using [nvm](https://github.com/nvm-sh/nvm). Refer to that project to install it and then you will be able to:
+
+ - Install any node version that you need:
+```
+nvm install 10.22.1
+nvm install 20.2.0
+```
+ - Then you will be able to switch between node versions:
+```
+nvm use 10.22.1
+node -v // will show v10.22.1 
+nvm use 20.2.0
+node -v // will show v20.2.0
+```
+
+As this project has a .nvmrc file you can call `nvm install` and `nvm use` without specifying the node version:
+```
+// being anywhere inside this project
+nvm install
+node -v // will show v10.22.1
+```
+
+
+### Complete sequence of commands
+
+Considering the above about having nvm installed on your system, here is the complete sequence of commands to generate pdf and epub files by yourself:
+
 ```
 git clone https://github.com/MostlyAdequate/mostly-adequate-guide.git
 cd mostly-adequate-guide/
+nvm install
 npm install
 npm run setup
 npm run generate-pdf

ch04.md

@@ -117,6 +117,7 @@ Should you prefer to do exercises directly in files using your own editor:
 
 - clone the repository (`git clone git@github.com:MostlyAdequate/mostly-adequate-guide.git`)
 - go in the *exercises* section (`cd mostly-adequate-guide/exercises`)
+- be sure to be using the recommended node version v10.22.1 (e.g. `nvm install`). More on this in [the readme of the book](./README.md#about-the-nodejs-version)
 - install the necessary plumbing using [npm](https://docs.npmjs.com/downloading-and-installing-node-js-and-npm) (`npm install`)
 - complete answers by modifying the files named *exercise\_\** in the corresponding chapter's folder 
 - run the correction with npm (e.g. `npm run ch04`)

exercises/README.md

@@ -31,6 +31,8 @@ your proposal can be verified by running:
 npm run ch04
 ```
 
+Remember to first install node dependencies being at the recommended node version of the project. More on this on [the main README of the project](../README.md#about-the-nodejs-version).
+
 Alternatively, you can also have a peak at the corresponding solution file: in this case
 `solution_a.js`.